Magnetic thin film heads for use in mass storage systems such as disk drives are known in the prior art. Many thin film heads include a single inductive element thereon which is used for writing data to the spinning magnetic disk and for reading data from the spinning magnetic disk. In the case of writing data, an electrical signal is applied to a conductor coil (the inductive element). A top pole and a bottom pole on either side of the conductor coil help to focus the magnetic field induced by the current flowing through the coil. The focused magnetic field is applied to the nearby moving magnetic medium. The magnetic field causes a magnetic signal representative of the electrical signal to be stored on the magnetic medium.
For reading data from the magnetic medium, the magnetic flux signal from the magnetic medium induces a magnetic flux signal between the top pole and bottom pole of the thin film head, which causes a magnetic flux signal to be applied to the conductor coil. This magnetic signal induces an electrical signal in the conductor coil which is representative of the magnetic signal recorded on the moving magnetic medium.
Since the read and write operations necessarily involve inducing signals in two opposite directions between a moving magnetic medium and a conductor coil, the single element inductive head is a compromised design which may be less than optimal for read operations and less then optimal for write operations.
The need for this compromise has been reduced in recent years with the development of thin film heads which employ magneto-resistive technology for the read function and a separate head employing standard inductive technology for the write function. In this manner, the separate heads can be optimized. The magneto-resistive (MR) element includes a nickel-iron (NiFe) film which changes its electrical resistance as a function of the strength of the magnetic field to which it is exposed. A constant current signal can be applied to the MR element and the varying voltage signal obtained from the MR element is representative of the magnetic signal stored on the moving magnetic medium. In order to prevent the NiFe film from being affected by any magnetic field other than the fields produced by the moving magnetic medium, the NiFe film is sandwiched between an upper and lower shield. The upper shield of this MR element can also function as the lower pole of the inductive element, giving rise to the name "merged MR heads."
As with any thin film head device, the manufacture and production of the devices is optimized to produce high yields with a minimum of production costs and time. Typically, merged MR heads are fabricated by building or stacking up a variety of materials in the form of films on a wafer. Processes for applying the materials in the form of films include sputtering, plating, and other forms of deposition. There are many layers deposited on the wafer including shield layers, gap layers, MR layers, coil layers, and pole layers. On top of the top pole layer, an overcoat of aluminum oxide (Al.sub.2 O.sub.3) is sputtered. This Al.sub.2 O.sub.3 encapsulating layer serves to protect all of the active layers underneath from being exposed to the air, so as to protect them. This Al.sub.2 O.sub.3 layer adds typically 40 .times.10.sup.6 meters (40 micrometers, microns, or .mu.m.) to the stack, which may itself already be 15 microns thick. At appropriate positions on the thin film head, gold or copper metal studs are provided protruding upwardly from the stack and through the encapsulation layer. The encapsulation layer has to be so thick because of the existence of so many peaks and troughs due to the top pole and the studs. The upper surface of the encapsulation layer is inherently uneven and irregular, having sharp edges thereon. To eliminate these sharp edges prior to subsequent processes are applied to the head (such as cutting/dicing and slider processing) the encapsulation layer is then lapped back and polished with a slurry of alumina in base solution. This is a time-consuming and dirty process. The encapsulation layer deposition process may take as long as fourteen hours and much of the material deposited is subsequently wasted when the lapping back process is performed. Metal studs are then opened after lapping for attachment of bonding pads and conductors thereto to allow the electrical signals to be routed to and from the active elements of the thin film head. These gold or copper metal studs may be as tall as 35 microns, much of which is eliminated in the lapping back process. In addition, to create such tall studs, uniform columns of photoresist material must be applied, which is difficult in the photo process.
As can be appreciated, the processes of depositing the thick encapsulation layer and lapping back to expose the metal studs are time consuming, costly, and dirty. In particular, it may take as long as fourteen hours to deposit the encapsulation layer. This is the longest process of all of the individual processes utilized in fabricating the thin film head. In addition, the gold metal studs are costly and a significant portion of them is wasted in the lap back process. Also, the process of lapping back the layer produces excess material and can cause contamination, reducing the yields for production of the thin film heads.
U.S. Pat. No. 5,326,429 discloses a method for manufacturing thin film heads wherein studs are eliminated from the design by depositing the coils and bonding pads simultaneously. Vias are later etched through the alumina overcoat layer to expose the bonding pads. A liquid etchant of hydrofluoric (HF) acid in water is used to create the vias. Unfortunately, HF acid is a hazardous liquid that is undesirable to use in production. Also, a street and alley pattern of scribe-line grooves is etched across the wafer for sawing and machining the wafer into individual heads, or sliders. These grooves eliminate most alumina chipping due to stress and damage introduced by the sawing and machining operations.
It is known in the industry that manufacturing yields can be minimized in part by minimizing the stress on the wafers and the sliders. While there are many techniques used to reduce the stress, one relevant to the present invention is using a low bias voltage level on the wafer during the encapsulation layer deposition process. It has been generally believed that higher bias voltages would increase the stress and decrease the yield of usable products from the manufacturing process.
It is against this background, and the desire to solve the problems of and improve on the prior art, that the above invention has been developed.